This application claims priority to German Patent Application 100 11 978.6 filed on Mar. 11, 2000.
Not Applicable
In digital controls for model railways, digital information and, at the same time, the power supply voltage are transmitted via the same connection line, namely the track, from a central control unit to various individual electrical consumers. The control unit modulates the power supply voltage with a control signal for a decoder in each consumer. Moveable electrical consumers in the form of locomotives thus receive an address, a desired speed, actuating, switch and control information, or the like, as digital information. The decoders in the consumers which serve as receiving means for the digital information decode the control signals and control a motor or switching devices with the energy which is also transmitted via the track.
In the case of a stationary decoder, the same principle applies. In this case, a fixed wiring is used which is connected to the track. Stationary consumers are, for example, turnouts which are supplied with power, as well as, with control signals using the track voltage, and which are provided with an appropriate decoder for decoding the control signals.
This type of voltage transmission for the purpose of power supply as well as control, has always been unidirectional from the control unit to the consumer. Contact via the track, as is known, is subject to possible bad track contacts, bogeys, wheels, bad contact at turnouts and the like. The switching processes and transients in the decoders, as well as the wave form of the combined control and track supply signal itself can cause great interference and distortions with corresponding harmonics. As a result of these circumstances, the decoder in a locomotive might not receive the control signal at all, and on the other hand, a received control signal could be so distorted so that it can not be decoded correctly.
An object of the invention is to provide a method and device for the digital control of moveable and stationary electrical consumers of a model railway, which provide a more reliable control with limited technical effort while allowing for the relevant control norms and standards.
This object is solved by the subject matter of the independent claims. Further advantageous developments are defined in the subclaims. The invention as claimed provides a digital multi-train control with bidirectional data transmission between the consumers and the model railway""s central control unit. The bidirectional data transmission enables information to be sent from the consumer which information in the simplest case, represents an acknowledgement or receipt of the transmission of control information.
According to the main object of the invention there is provided a method for digital control of electrical consumers in a model railway wherein power for the consumers is supplied over the track in form of a square wave voltage signal which is frequency and/or pulse width modulated according to digital control information for the consumers generated by a central control unit of the model railway, and wherein a consumer, after having received a control information specifically addressed to said consumer, applies a return signal to the track, which return signal has a higher frequency than the frequency of the modulated square wave voltage, and wherein this return signal is detected by synchronising the detection to the square wave voltage such that the return signal is detected in periods of the square wave voltage signal which are free of signal edges. The consumers can be moveable and/or stationary electrical consumers.
A fundamental problem is solved in the invention. It is, in principle, very difficult to return or feed back a data signal from the decoder of a consumer to a control unit via the same transmission path as the track power supply. This is due to the above mentioned signal distortion within this transmission path and the resulting strong interference effects and distortions in the signal to be returned or fed back to the control unit. It is likewise very difficult to successfully decode the returned data, for example, in the form of an acknowledgement or receipt of a control signal. On the one hand, the control signal from the control unit, which is superimposed on the power supply voltage as frequency modulation or pulse width modulation in a predefined manner, is always transmitted and present, and must not by affected by the return signal. On the other hand, the strong control signal modulation in the track signal presents a problem for decoding the signal to be returned. Moreover, this is made even more difficult by the fact that particularly the decoder of the moveable consumer must be small sized due to its predefined constructional design in the consumer. Therefore, providing any substantial additional signal generating and transmitting equipment is ruled out.
The inventional solution succeeds in superimposing a return signal to be sent or retransmitted to the control unit on the track signal by means of little additional technical features within a decoder which have to be provided to implement this superimposing. Furthermore, the generated return signal can be produced reliably and with little technical effort. A decisive feature here is that the signal is generated and detected in synchronized manner to the modulated track signal such that the return signal can only be detected in signal periods of the track signal which do not comprise signal edges, and, in other words, in signal periods or signal intervals between alternating polarities.
Preferably, the time sections of the modulated track signal being used for superimposing the return signal are time sections in which the voltage level of the digital track signal does not change. Preferably, these sections correspond with the second signal half of a zero information in the digital track signal, as shown below. These periods are detected by the decoder""s evaluator means when detecting the digital track signal anyway, so that a corresponding control or trigger signal can be derived from the evaluator unit for generating the return signal without extra effort.
The return or feedback signal itself is a high frequency signal whose frequency is considerably higher than the modulation frequency of the track signal. Such a high frequency signal can be detected reliably in the above mentioned signal edge free periods between alternating polarities of the track signal. The criteria for this are explained below referring to the disclosed examples. The signal form of the return signal to be superimposed on the track signal is not restricted to specific wave forms. For example, the digital track signal can be superimposed with a 1 MHz oscillation generated by an oscillator. Preferably, a cost-effective and space-saving current modulation is used rather than a voltage coupling by means of an oscillating circuit or capacitors.
In principle, the high frequency return signal can also be coupled into signal sections of the track signal which are not free of signal edges by the consumer, since, as recited in claim 1, upon receipt of the return signal, the signal periods which comprise signal edges are cut off In this way, the oscillating circuits or the active filters of high quality in the detection means for the return signal, which are tuned to the return signal""s frequency, remain unaffected by the control signal edges of the square wave track signal. However, it is advantageous when the return signal is exclusively generated in the predefined edge free periods of the track signal. Thereby, the lost power is kept to a minimum.
An addressed consumer, to which control information is sent or transmitted in a track voltage data packet cannot only acknowledge the receipt of the control information by generating the return signal intermittently or continuously and preferably in the next data packet. The consumer can even send more information in several of the periods between signal edged or alternating polarities available in the next data packet, as explained in detail below.
The next data packet is preferably used for transmitting the return signal because this guarantees that the return signal is clearly allocated to the returning consumer which was addressed in the previous packet so that a separate address in the return signal is not necessary to identify the returning consumer which generated the return signal.
As a result of the receipt message provided by the return signal, the control through the central control unit becomes more secure against the above mentioned influence by signal interference and distortion. Multiple transmissions of the same control information for one consumer can be avoided. Hence, lots of control information for a number of consumers can be managed, thereby increasing the transmission bandwidth of the control unit. As a result of the bidirectional communication according to the invention, it is also possible to transmit consumer data to the central control unit via the track, alongside the transmission of supply energy and control information, at the same time as transmitting control information to the consumers.
In addition, the invention offers a simple way to localize moveable consumers on the model railway. For this purpose, the track is subdivided into several sections, with an evaluation unit allocated to each section.
The invention has been implemented for data transmission in the NMRA DCC Electrical Standard and NMRA DCC Communication Standard, however, it can also be used for other forms of digital transmission of information from a control unit to a consumer in a digital model railway if energy is simultaneously supplied via the same wiring or transmission means as the control information. For example, this is the case for standards with pulse width or pulse length modulation instead of the frequency modulation used in the preferred embodiment. Typically, regardless of the standard, an information packet sent to a consumer contains its address so that the data""s addressee is clearly defined. The invention, however, could also be used in principle with a control system where a fixed number of possible consumers receive information in a prescribed addressing cycle.
An evaluation means for the return signal from the consumer can, for example, be integrated into a power amplifier or into the control unit on the railway, or can be provided as an independent additional device. The evaluation means synchronizes the data from the return signal which the consumer sends by detecting and evaluating the return signal together with the track signal which the control unit transmits. As a result of this, the synchronisation of the consumer""s return signal is achieved. Synchronisation can also be achieved by sending a specific synchronisation signal from the control unit directly to the evaluation means. In this way, the answer from a specific consumer can be triggered.
Furthermore, in principle, it is also possible to implement the invention by generating a constant additional high frequency signal in the track signal corresponding to the frequency of the above return signal and, instead of generating the return signal, a xe2x80x9creturningxe2x80x9d consumer would temporarily damp or suppress this continuous high frequency signal. For detecting such a signal suppression, the evaluation means can also comprise a sender or transmitter which constantly modulates a sender frequency, e.g. 1 MHz, on the track voltage and which monitors the amplitude of the modulated voltage. Synchronisation of the return signal can be realized as described above. A consumer which transmits a return signal to the evaluation unit loads the track voltage during the predefined transmitting or sending periods by lowering its impedance at 1 MHz. The evaluation unit detects the resulting amplitude decrease and recognizes a return signal. Thereby, a binary transmission of information from the consumer to the control unit is also possible by means of repeated load and non-load actions effected in the preferred predefined time periods.
These and still other objects and advantages of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described in reference to the accompanying drawings. These embodiments do not represent the full scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.